Control apparatus and method for a vehicle automatic transmission to suppress shock upon changing speed

ABSTRACT

An apparatus for controlling an automatic transmission of an automobile and a control method thereof. When a feedback control is executed by the automatic transmission while the speed is being changed, the control operation may often lose stability. This is due to a large deviation between a target value and a practical value at the start of the feedback control operation being caused by a change in the opening degree of the throttle and a change in the oil temperature in the automatic transmission. To solve such a technical problem, the invention employs a control apparatus which detects that the automatic transmission is changing the speed, operates the output shaft torque of the automatic transmission, recognizes a point of inflection of the output shaft torque while the speed is being changed, sets a target output shaft torque of the automatic transmission, and sets an initial target value at a moment of said point of inflection.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a control apparatus for anautomatic transmission, which controls the oil pressure for operatingthe clutch for changing the speed of the automatic transmission of avehicle, and to a control method.

[0003] 2. Prior Art

[0004] According to a conventional control method of this type as taughtin, for example, Japanese Patent Laid-Open No. 25662/1992, the operationoil pressure to be supplied to a friction coupling device has beencontrolled by learning, so that a deviation decreases between a targetvalue of change in the torque and a practical value at the start of thefeedback control operation.

[0005] According to the control method taught in Japanese PatentLaid-Open No. 25662/1992, however, the deviation increases due to achange in the opening degree of the throttle and a change in the oiltemperature in the automatic transmission, leaving a problem in that thecontrol stability is impaired in the feedback control operation when thespeed is being changed.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide an apparatus forcontrolling a transmission which suppresses a shock in the change ofspeed by bringing a target value of change in the torque into agreementwith a practical value at the start of the feedback control operation,and a method thereof.

[0007] There occurs a hunting or a change in the torque when a deviationis great between a target value and a practical value at the time ofstarting the feedback control operation. In the conventional feedbackoperation for controlling the transmission, the oil pressure fed to afriction coupling device is brought into match, so that the deviationdecreases between the two. However, the practical oil pressurefluctuates with respect to the instructed oil pressure due to accuracyof the actuator. Namely, the feedback control operation loses stabilitydue to a fluctuation in the oil pressure. It has, therefore, been urgedto provide an actuator having improved accuracy. According to thepresent invention, however, there does not occur a deviation between thetwo since a practical torque value is used as an initial target value.This permits the operation oil pressure to be roughly set to someextent, making it possible to use an actuator that is constructed at alower cost.

[0008] According to the present invention, the above-mentioned problemis solved by an apparatus that is described below. That is, the presentinvention provides an apparatus for controlling the oil pressure of anautomatic transmission, having a pressure-regulating instructiongenerating means which changes the speed by coupling or decoupling apredetermined friction coupling device in the automatic transmissioncoupled to an engine, regulates the oil pressure that acts on saidfriction coupling device at the time of changing the speed, and changesthe pressure-regulating characteristics, and means for so controllingthe output shaft torque of said automatic transmission as to follow atarget value, said apparatus for controlling the oil pressure of theautomatic transmission further comprising:

[0009] a speed-changing detecting means for detecting that saidautomatic transmission is changing the speed;

[0010] a torque operation means for operating the output shaft torque ofsaid automatic transmission;

[0011] a point-of-inflection recognizing means for recognizing a pointof inflection of the output shaft torque during the change of the speed;

[0012] a target value-setting means for setting a target value of theoutput shaft torque of said automatic transmission; and

[0013] an initial value-setting means for setting said initial targetvalue at a moment of said point of inflection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a diagram illustrating the constitution of a firstembodiment of the present invention;

[0015]FIG. 2 is a time chart at the time of shift-up;

[0016]FIG. 3 is a time chart at the time of shift-down;

[0017]FIG. 4 is a diagram illustrating the constitution of a secondembodiment of the present invention;

[0018]FIG. 5 is a time chart at the time of shift-up; and

[0019]FIG. 6 is a diagram of characteristics illustrating the amount ofcorrection of a target torque.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the present invention will now be described indetail with reference to the drawings.

[0021]FIG. 1 is a diagram illustrating the constitution according to afirst embodiment of the present invention. An engine 101 in thisembodiment has four cylinders. The engine 101 is equipped with anignition device 102. The ignition device 102 has four spark plugs 103 tocorrespond to the number of the cylinders in the engine 101. An intakepipe 104 for introducing the air into the engine 101 is provided with anelectronically controlled throttle 105 for regulating the flow rate ofthe air that passes therethrough, a fuel injection device 106 forinjecting the fuel, and an air flow meter 107. The fuel injection device106 has four fuel injection valves 108 to correspond to the number ofthe cylinders in the engine 101.

[0022] The electronically controlled throttle 105 is the one in which athrottle valve 110 is driven by an actuator 109 to control the flow rateof the air. In an ordinary automobile, the throttle valve 110 and theaccelerator pedal (not shown) are coupled together through a mechanicalwire (not shown), so as to operate in a one-to-one manner.

[0023] A fly-wheel 112 is attached to a crank shaft 111 of the engine101. An engine revolution sensor 113 is attached to the fly-wheel 112 todetect the number of revolutions of the crank shaft 111, i.e., to detectthe running speed Ne of the engine. A torque converter 114 directlycoupled to the fly-wheel 112 includes a pump 115, a turbine 116, and astator 117. The output shaft of the turbine 116, i.e., the output shaft118 of the torque converter, is directly coupled to a steppedtransmission mechanism 119. The output shaft 118 of the torque converteris equipped with a turbine revolution sensor 120 for measuring therevolution speed Nt of the turbine.

[0024] The transmission mechanism 119 is constituted by a planetary gear121, and friction coupling devices 122 and 123. Upon coupling ordecoupling the devices 122 and 123, the gear ratio of the gear 121 ischanged to change the speed. These devices 122 and 123 are controlled byspool valves 126, 127 and linear solenoids 128, 129 (pressure-regulatingdevices). The transmission mechanism 119 is coupled to the output shaft124.

[0025] Furthermore, the output shaft 124 of the transmission is equippedwith a vehicle speed sensor 125 for detecting the revolution speed No ofthe output shaft. An automatic transmission 130 is constituted by theseparts.

[0026] The above-mentioned engine 101 and the actuator for driving theautomatic transmission 130 are controlled by a controller 131. Thecontroller 131 receives a throttle opening degree θ, revolution speed Noof the output shaft of the transmission (may be replaced by anacceleration sensor by using differential signals), revolution speed Ntof the turbine, revolution speed No of the engine, oil temperature Toilof the transmission, depressed amount a of the accelerator pedal, etc.,and uses them for effecting the control operation.

[0027] In a special system, the output shaft torque To of thetransmission detected by a torque sensor (not shown) attached to theoutput shaft 124 of the transmission, is received by the controller 131.Furthermore, a signal of an acceleration sensor (not shown) mounted onthe vehicle exhibits the same waveform as the above-mentioned torquesensor signal and can, hence, be used for controlling the frictioncoupling devices of the present invention.

[0028] As an example, a torque operation means 132 in the controller 131operates the output shaft torque of the transmission. As the torqueoperation means, there can be exemplified an acceleration sensor signal,torque sensor signal, etc. as described above. There can be furtherexemplified an estimated torque value operated from Ne, Nt and torqueconverter characteristics that pertain to the prior art, and anestimated torque value found from a correlation to the difference of No.

[0029] Next, the during-the-change-of-speed detecting means 133 detectswhether the automatic transmission is changing the speed or not byusing, for example, the ratio of revolution speeds between the inputshaft and output shaft of the transmission or the so-called gear ratio.The point-of-inflection recognizing means 134 recognizes a point ofinflection on the torque of the output shaft during the change of thespeed. As this means, use can be made of a method which uses a change inthe torque found by the torque operation means or a method of detectinga timing at which the gear ratio assumes a desired value. Here, when apoint of inflection is recognized during the change of the speed, theinitial value-setting means 135 sets the value found by the torqueoperation means 132 as an initial value. A target value-setting means136 sets an ideal waveform of a change in the torque during the changeof the speed as a target value.

[0030] Next, a comparator means 137 operates a deviation between thetarget value that is set as described above and a practical torque foundby the torque operation means 132. By using a deviation operated by thecomparator means, a correction value operation means 138 finds an amountof correction for feedback control. Based upon the amount of correctionfound by the correction value operation means 138, a pressure-regulatinginstruction generating means 139 outputs a pressure-regulatinginstruction to the actuator, so that a change in the torque during thechange of the speed will follow the target value.

[0031]FIG. 2 is a time chart of signals at the time of shift up and ofphysical quantities. The following description deals with the case ofchanging the second gear to the third gear. When a change-of-speedinstruction signal changes from a second gear to a third gear, an oilpressure instruction value (HC) of the coupling side is raised to amaximum instruction value. This is to fill the clutch chamber with anoil to improve control performance, and to shorten the time from thegeneration of the change-of-speed instruction signal to the start ofchange of the speed.

[0032] After the oil has been charged, the oil pressure instruction HCis set to a value at which the accelerations are in agreement at pointsa and b in the drawing. This instruction value is set based upon aphysical formula consisting of an input torque of the clutch and therevolution speed. The torque phase starts with an increase in the oilpressure on the coupling side as instructed. As the torque phase startsand the clutch of the decoupling side is decoupled, the inertial phaseis introduced.

[0033] In the inertial phase, the inertial energy increases, and anestimated torque assumes a waveform as shown. Here, a targetacceleration is set to suppress the shock in the change of the speed,and the oil pressure of the coupling side is controlled by feedback, sothat a practical estimated torque approaches the target value.

[0034] Here, an estimated change of torque (dT_est) has been operatedand when it is recognized that the value dT_est is lower than theLevel_(—)1 during the change of the speed, the target value of theabove-mentioned feedback control operation is set. A value detected by achange-of-torque detecting means is used as the initial target value.Therefore, the target value at the start of the feedback controloperation is necessarily in agreement with the practical value, andthere exists no deviation between the two, contributing to enhancing theperformance for following the target value in the feedback controloperation.

[0035]FIG. 3 is a time chart of signals at the time of shift down and ofphysical quantities. The following description deals with the case ofchanging the third gear to the second gear. When the change-of-speedinstruction signal changes from the third gear to the second gear, theoil pressure instruction (HC) of the coupling side is set to a valuebased upon a physical formula determined by an input torque of theclutch and the revolution speed. Accompanying a shifted-down clutch ofthe decoupling side, the clutch of the decoupling side starts beingdecoupled and the inertial phase starts. Here, when there is no feedbackcontrol, the torque decreases with an increase in the revolution speedas shown in FIG. 3. The oil pressure of the decoupling side iscontrolled by feedback so that the estimated torque approaches thetarget value.

[0036] Like the case of the shift up, the target value is set by usingan estimated change rate of torque (dT_est) when dT_est is lower thanthe Level 2 during the change of the speed. Therefore, there occurs nodeviation between an actual valueof an estimated torque and the targetvalue at the start of the feedback control operation, contributing toenhancing the targe-following performance.

[0037]FIG. 4 is a diagram illustrating the constitution according to asecond embodiment of the present invention, FIG. 5 is a time chart whenthe accelerator pedal is depressed during the shift-up, and FIG. 6 is adiagram of characteristics illustrating the amount of correcting thetarget torque.

[0038] Referring to FIG. 4, the same mechanisms as those of FIG. 1 arenot described here again. A throttle-opening-degree detecting means 140detects the opening degree of the throttle valve. When the detectedopening degree of the throttle valve has changed while the automatictransmission is changing the speed, an amount-of-correction operationmeans 141 corrects the target value that is set by the targetvalue-setting means 136. The amount of correction is determineddepending upon a change in the opening degree of the throttle valveduring the change of the speed as shown in FIG. 6.

[0039] Referring to FIG. 5, described below is the case of changing thesecond gear to the third gear. In the feedback control operation asdescribed above, the practically estimated torque value is set as aninitial target value. In the phase 1 during the change of the speed, thefeedback control operation is carried out so that an ordinary targetvalue is set and the practically estimated torque follows the targetvalue.

[0040] Here, in the phase 2 where the accelerator pedal is depressed andthe opening degree of the throttle valve changes from θ1 to θ2, theinput torque of the clutch increases and, hence, the clutch is notcoupled and the speed does not change. That is, when the pedal valve isdepressed during the change of the speed, the oil pressure of thecoupling side must be elevated so that the clutch is coupled. Dependingupon a change in the opening degree of the throttle valve, therefore,the target value is corrected and the feedback control operation isexecuted to obtain favorable speed-change characteristics even under theabove-mentioned operation conditions.

[0041] As described above, the present invention solves the problem inthat a deviation increases between a target value and a practical valueat the start of the feedback control operation due to a change in theopening degree of the throttle valve and a change in the oil temperaturein the automatic transmission impairing the stability in the feedbackcontrol operation during the change of the speed. Namely, the inventionbrings a target value in the change of the torque into agreement with apractical value at the start of the feedback control operation, makingit possible to suppress a shock during the change of the speed, which isan excellent effect.

What is claimed is:
 1. An apparatus for controlling an automatictransmission having a pressure-regulating instruction generator whichchanges the speed by coupling or decoupling a predetermined frictioncoupling device in the automatic transmission coupled to an engine,regulates the oil pressure that acts on said friction coupling device atthe time of changing the speed, and changes the pressure-regulatingcharacteristics, comprising: a speed-changing recognizing means forrecognizing that said automatic transmission is changing the speed; atorque calculation means for calculating the output shaft torque of saidautomatic transmission when a speed-changing is recognized by thespeed-changing recognizing means; a point-of-inflection recognizingmeans for recognizing a point of inflection in the output shaft torqueof said transmission; a target value-setting means for setting a targetvalue of the output shaft torque of said transmission; an initialvalue-setting means for setting said initial target value at a moment ofsaid point of inflection; and a transmission output shaft torqueinstruction means for outputting an instruction to saidpressure-regulating instruction generator so that said output shafttorque of said transmission follows said target value.
 2. An apparatusfor controlling an automatic transmission according to claim 1, whereinsaid point-of-inflection recognizing means recognizes said point ofinflection based upon a change rate of the output shaft torque of saidtransmission.
 3. An apparatus for controlling an automatic transmissionaccording to claim 1, wherein said point-of-inflection recognizing meansrecognizes said point of inflection based upon a ratio between the inputand output revolution speeds of the transmission.
 4. An apparatus forcontrolling an automatic transmission according to claim 1, furthercomprising: a throttle-opening-degree detector for detecting the openingdegree of the throttle that is varied by the acceleration pedaloperation by a driver; and an amount-of-correction calculating means forcalculating the amount of correction for said target value dependingupon a change in the opening degree of the throttle from saidthrottle-opening-degree detector.
 5. A method of controlling anautomatic transmission having a pressure-regulating instructiongenerator which changes the speed by coupling or decoupling apredetermined friction coupling device in the automatic transmissioncoupled to an engine, regulates the oil pressure that acts on saidfriction coupling device at the time of changing the speed, and changesthe pressure-regulating characteristics, wherein: when said automatictransmission is changing the speed, the output shaft torque of saidautomatic transmission is calculated; a point of inflection of theoutput shaft torque of said transmission is recognized; a target valueof the output shaft torque of the transmission is set, and said initialtarget value is set at a moment of said point of inflection; and aninstruction is output to said pressure-regulating instruction generator,so that said output shaft torque of the transmission follows said targetvalue.
 6. An method of controlling an automatic transmission accordingto claim 5, wherein said point-of-inflection is recognized based upon achange rate of the output shaft torque of said transmission.
 7. A methodof controlling an automatic transmission according to claim 5, whereinsaid point-of-inflection is recognized based upon a ratio between theinput and output revolution speeds of the transmission.
 8. A method ofcontrolling an automatic transmission according to claim 5, wherein theamount of correction for said target value is calculated depending upona change in the opening degree of the throttle that is varied by theacceleration pedal operation by a driver.